The fan blows but the rear air is not cold on my 2006 Durango

Have you checked the blower motor for power and ground ?

Its supposed to blow out only cold air. I wondered the same thing when I purchased my 2001 durango and then I read the owners manual and it says it is only supposed to blow cold air out in the rear of the vehicle.

remove the fan and check the fan impeller for debrea

Check the aux water pump has power. The pump is locate on right side of engine compartment, between engine and frame. check terminal for corrosion.

ok, missed the part about the rear ac working, the part that causes this is called the air temperature control blend door actuator motor, it is an electric motor driven gear drive that moves the plastic door inside the air ducking to mix or shut off the hot or cold air from the ac evaporator core or the heater core, you will need to replace it.

This is a common problem and the solution usually is that the fron thermostat is usually gone and needs replaising. Shouldn't be too much money to get done. It's just not opening up to let the cold air pass into the from area but the rear one is working fine which allows it to blow cold air.

the resister block needs changing... oddly enough i'm unsure of what fan you are saying is not working.... if it's the front.. the resister block is located on the duct work under the dash for the air... near the fan... you will see a connector going into the side of the duct work. two screws and the block comes out... should be fairly obvious for the rear one but it will be near the fan.

The rear vent system has a separate heater core/blower system. heater core could be plugged up or the coolant lines going to rear heater core are plugged. could also be low coolant/faulty water pump not producing enough pressure, or air in the cooling system which will need to be bled if so.

thats because it taking air from outside and the secltor must of jumped a notch

blower motor resistor maybe why it only blows on high